PDO: Move online schema creation behind feature flag

The XHGui install at Wikimedia Foundation is deployed with database
credentials that permit read-write operations (SELECT, INSERT) but
as safety precaution do not permit admin actions like CREATE from
individual web requests. In addition to not allowing admin actions,
our install also disallows DELETE queries, given that the install
is exposed to the public Internet (ref perftools#248)
and further disables POST requests (so that those features serve
HTTP 40x instead of a db query error with HTTP 50x).

Since XHGui version 0.16.0, with perftools#355,
the lazy-creation for tables was moved from the Saver code (which is
not used when browsing XHGui) to to Repo code, and thus resulted in
the application serving HTTP 500 on all requests, unless the
`CREATE TABLE` query is permitted on all web requests.

Fix this by making this method call feature flagged in a way that
can be disabled using XHGUI_PDO_INITSCHEMA=false.

Change-Id: I681d500fd393a47471a475b705c67280b39ab7ce

config/config.default.php

@@ -18,6 +18,7 @@
         'pass' => getenv('XHGUI_PDO_PASS') ?: null,
         'table' => getenv('XHGUI_PDO_TABLE') ?: 'results',
         'tableWatch' => getenv('XHGUI_PDO_TABLE_WATCHES') ?: 'watches',
+        'initSchema' => getenv('XHGUI_PDO_INITSCHEMA') ?: 'true',
     ],
 
     // Database options for MongoDB.

src/Db/PdoRepository.php

@@ -34,7 +34,6 @@ public function __construct(PDO $pdo, string $driverName, string $table, string
         $this->driverName = $driverName;
         $this->table = sprintf('"%s"', $table);
         $this->tableWatches = sprintf('"%s"', $tableWatch);
-        $this->initSchema();
     }
 
     public function getLatest(): array

src/ServiceProvider/PdoStorageProvider.php

@@ -48,12 +48,16 @@ public function register(Container $app): void
         };
 
         $app[PdoRepository::class] = static function ($app) {
-            return new PdoRepository(
+            $repo = new PdoRepository(
                 $app['pdo'],
                 $app['pdo.driver'],
                 $app['config']['pdo']['table'],
                 $app['config']['pdo']['tableWatch']
             );
+            if ($app['config']['pdo']['initSchema'] === 'true') {
+                $repo->initSchema();
+            }
+            return $repo;
         };
 
         $app['searcher.pdo'] = static function ($app) {